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Old 6th October 2010, 09:34 AM   #1021
AndrewT is offline AndrewT  Scotland
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post1016.
Scott Wurcer's comparison table seems to offer fair comparison.

The manufacturer's extracted data, shown in the post, uses different test conditions and cannot be used for comparison purposes.

The sk170 is designed and specified for audio use.
The f862 is designed and specified for RF use.
Yes, the f862 can be used for audio, but then it's audio performance should be compared to the sk170 jFETs.

What did Rick NL measure? I suspect he measured Idss. This is OK for building B1, but this is not matching.
2SK170 matching

Rick refers to B1 on a chip
Even here Euvl commpares using manufacturer's data.
B1-Turbo on a Chip
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Last edited by AndrewT; 6th October 2010 at 09:41 AM.
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Old 6th October 2010, 09:48 AM   #1022
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Quote:
Originally Posted by AndrewT View Post
post1016.
Hi Andrew. I guess you refer to me.

For En k170 and bf862 in its datasheets have a different measurement units. Don't know if they are crucially different.
Here is sound experience comparison: BF862 Preamp
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Last edited by AndriyOL; 6th October 2010 at 10:03 AM.
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Old 6th October 2010, 10:09 AM   #1023
AndrewT is offline AndrewT  Scotland
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Originally Posted by AndriyOL View Post
For En k170 and bf862 in its datasheets have a different measurement units. Don't know if they are crucially different.
it's not the measurement units, they are the same.

It's the operating conditions that are different and these different conditions do result in different measurement data.

Look at the graph of transconductance vs Id for the f862 and sk170. They are almost superimposible. No where near the 2:1 difference quoted in the headline data shown.
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Last edited by AndrewT; 6th October 2010 at 10:11 AM.
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Old 6th October 2010, 10:30 AM   #1024
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You're right. But I meant nV/Hz1\2 for sk170 and nV/VHz for bf862, if you understand what I'm about. I don't have these symbols on keyboard.
What you mean "superimposible"? Yes, Yfs under equal measurement conditions ought to be the same. In Scoutt Wurcer's table they are slightly different.
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Last edited by AndriyOL; 6th October 2010 at 10:47 AM.
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Old 6th October 2010, 11:04 AM   #1025
AndrewT is offline AndrewT  Scotland
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Originally Posted by AndriyOL View Post
You're right. But I meant nV/Hz1\2 for sk170 and nV/VHz for bf862, if you understand what I'm about.
noise performance.
Yes the f862 is designed to be low noise at high frequencies.
The sk170 is designed to be low noise at audio frequencies.
The f862 does have good noise performance for an RF device right down to 1kHz and even pretty reasonable at 100Hz.

Superimpose = place one on top of the other. Scott recognised this and that's why he quoted the data he showed for comparison.

If you look at Id = 5mA and 10mA and 20mA you will see that the RF and AF jFETs perform almost identically for transconductance.
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Old 6th October 2010, 11:41 AM   #1026
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Quote:
Originally Posted by AndrewT View Post
noise performance.
I'm about measurement unit. They are a little bit different for both devices regarding Hz in En.
Quote:
Originally Posted by AndrewT View Post
The f862 does have good noise performance for an RF device right down to 1kHz and even pretty reasonable at 100Hz.
If you look at Id = 5mA and 10mA and 20mA you will see that the RF and AF jFETs perform almost identically for transconductance.
I would say it has better Nf except at 10Hz.
It's good enough that bf at this parameter isn't worse than sk.
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Old 6th October 2010, 12:55 PM   #1027
juma is offline juma  Germany
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... and even pretty reasonable at 100Hz. ...
Yeah, if the "best of the bunch" and "even pretty reasonable" were synonymous phrases...
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Old 6th October 2010, 02:43 PM   #1028
housing is offline housing  Hong Kong
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AndriyOL,

If you want to use BF862 instead of 2SK170, try it yourself. Nobody has built a RMI-FC100 using BF in the front end so we can't help you out in this respect. Better still, build the 2SK170 version also and compare. Please don't forget to report back your findings here.

Thank you very much.

housing

Last edited by housing; 6th October 2010 at 02:56 PM.
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Old 6th October 2010, 03:26 PM   #1029
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AndriyOL,
If you want to use BF862 instead of 2SK170, try it yourself. Nobody has built a RMI-FC100 using BF in the front end so we can't help you out in this respect. Better still, build the 2SK170 version also and compare. Please don't forget to report back your findings here.
Thank you very much.
housing
I'll report results without doubt, which have to be astonishing as I suspect, if I do this challenge. But I'm still collecting parts and don't have found output devices where to buy yet.
Maybe you know what value of grid stopper resistor shall I use (try to use) with bf or it will be ok with R27 2k?
Regards.
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Last edited by AndriyOL; 6th October 2010 at 03:30 PM.
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Old 14th October 2010, 05:49 PM   #1030
TedS is offline TedS  United States
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Originally Posted by Sheldon View Post
Ok, let's get started then. I recommend the front end supply as a good place to begin.

Sheldon
Hi Sheldon,

It's taking me some time, but I'm trying to get spun back up on this. I've collected my boards and parts, and this is what I found:

Caps - I have everything except C1-4 for the PSU board. Someone suggested they were unnecessary, I guess.

Resistors - I have most, but not all.

Transistors - I have a matched set of J1 & J2 from AndrewT
I have 5 each of MJE15034/MJE15035, but need to match
I have ~15 each of NJL, but need to match

I do not have the BC550C, BC560C, 2SC or 2SA parts - I was waiting for someone who had said they would offer matched sets of these, but it appears they may no longer be interested.

Misc. - I don't have any diodes, pots, fuses, etc.

My plan is to simply start stuffing my boards with the parts I do have, and make a list of needed items as I go. I'll probably ask for input before ordering anything, and I'll need help with some of the matching. At least this way I'll build some momentum on the project. Any thoughts or suggestions?

Ted
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